In transceivers, a bias voltage is required for biasing transistors, in particular for radio-frequency (RF) power amplifiers. With a bias voltage of this type, it is possible for example to set an operating point of transistors of the power amplifier in order to ensure a good linearity of the power amplifier. This can contribute to increasing a data throughput in a communication channel.
One aim here is for a drain current of a radio-frequency power amplifier, if no radio-frequency signal is present (also referred to quiescent drain current), to be kept constant as far as possible, which ensures that the power amplifier operates with desired properties.
However, since various system parameters vary during the lifetime of a transceiver, in particular of a power amplifier (for example a temperature at which the amplifier operates, or changes on account of a drift of components of the amplifier), adaptive biasing is desirable in order as far as possible to ensure the desired properties of the amplifier even in the event of such changes in system parameters.
During transmission operation of the power amplifier of a transceiver, at an input of a transistor biased with the bias voltage there is not just the bias voltage present, rather a radio-frequency signal to be transmitted is superposed on said bias voltage. Therefore, in this state it is difficult to measure the drain quiescent current (i.e. the drain current of the transistor on account of the bias voltage without a radio-frequency signal present) and to control the bias voltage on the basis of the measurement. In conventional transceivers, however, the power amplifier is normally in operation, and so essentially a setting or control of the bias voltage can take place only infrequently, for example upon start-up of the power amplifier. Control of the bias voltage in the course of operation of the transceiver would be desirable on the other hand, however, in order to be able to continuously ensure the desired properties of the transceiver, for example of a power amplifier thereof.
It is an object of the present application to provide corresponding methods for providing a bias voltage, devices for providing a bias voltage, and corresponding transceivers, in which this problem is eliminated or at least alleviated.